Accretion definition, an increase by natural growth or by gradual external addition; growth in size or extent. See more.
Alveoli are tiny sacs within our lungs that allow oxygen and carbon dioxide to move between the lungs and bloodstream. Learn more about how they function and quiz your knowledge at the end.
1 Describe the changes in the type of epithelium throughout the respiratory system. 2  Explain how the structure of different segments of the respiratory airways reflect the functional roles that these airways play in air movement and gas exchange.espiratory bronchioles also have cuboidal epithelia, but contain some alveoli. Alveolar Sac and Alveolus: An alveolar sac contains many alveoli. Type I and Type II Pneumocyte: Type I pneumocytes are squamous cells that support gas exchange; type II pneumocytes are cuboidal and create pulmonary surfactant.